You need to write a volumetric renderer. You can extract a surface from the voxel data. You can do this by simply using cubes (like Minecraft, see http://codeflow.org/entries/2010/dec...s-in-opengl-4/) or you can use something more complex that gives nicer results like Marching Cubes or Surface Nets.

Alternatively, you can ray cast the voxel data in a fragment shader after loading the layered images into a 3D texture.